feat(ui): add configurable sidebar display

[skaragianis]

I often turn on the sidebar to keep an eye on agent activity and scope. This makes it a configuration.

Adds --sidebar and --no-sidebar CLI flags, and a sidebar configuration with options "auto", true, and false. Default remains auto. true will not override pager mode or the responsive layout. false will override the responsive layout. An 's' keypress continues to toggle where the responsive layout allows.

Addresses (#514)

[greptile-apps]

PR author is not in the allowed authors list.

[vercel]

@skaragianis is attempting to deploy a commit to the Modem Team on Vercel.

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[skaragianis]

bun check:docs now passes on 7b1b2a4, if you could approve the pending runs on 8294f57 please.

[skaragianis]

I rebased on main to resolve the conflict with #675 and cleaned up the formatter churn I accidentally left in App.tsx (which is what caused the conflict). No change to the feature itself - the diff is the same minus the whitespace. If you could kick it along again please?

[skaragianis]

@benvinegar will you be swinging past again?

[benvinegar]

Thanks for the follow-up. The feature looks sound on its original base, and the current head passes typecheck, the targeted tests, and the generated-docs check. Two things need addressing before merge:

1. Please rebase onto current main. #757 changed s to toggle only the active files pane, while this PR's sidebarState still filters every left/right pane through effectiveOpenPaneKeys. Resolving the App.tsx conflict mechanically would regress independently opened extension panes. Please apply the configured initial state to the files-pane slot/open state while preserving other extension panes, with coverage for the combined behavior.
2. buildCommonOptions scans the full raw argv, including pathspecs after --. As a result, hunk diff -- --sidebar and hunk diff -- --no-sidebar both keep the pathspec and change sidebar state. Please resolve these flags only from command-option tokens before the separator and add a regression test.

This comment was generated by Pi using gpt-5.6-sol

[benvinegar]

Rebased onto current main and addressed both findings. The sidebar preference now controls only the active files-pane slot while preserving independent extension panes, including replacements. Paired boolean flags also stop at the -- separator, with table-driven regression coverage.

This comment was generated by Pi using gpt-5.6-sol

[jesseleite]

Just wanted to say thank you both for this one! 🎉